In deepwater drilling rigs, marine risers extending from a wellhead fixed on the ocean floor have been used to circulate drilling fluid back to a structure or rig. The riser must be large enough in internal diameter to accommodate the largest bit and pipe that will be used in drilling a borehole. During the drilling process drilling fluid or mud fills the riser and wellbore.
An example of a drilling rig and various drilling components is shown in FIG. 1 of U.S. Pat. No. 6,263,982 (which patent is incorporated herein by reference). A conventional slip or telescopic joint SJ, comprising an outer barrel OB and an inner barrel IB with a pressure seal therebetween can be used to compensate for the relative vertical movement or heave between the floating rig and the fixed subsea riser R. A Diverter D can been connected between the top inner barrel IB of the slip joint SJ and the floating structure or rig S to control gas accumulations in the riser R or low pressure formation gas from venting to the rig floor F. A ball joint BJ between the diverter D and the riser R can compensate for other relative movement (horizontal and rotational) or pitch and roll of the floating structure S and the riser R (which is fixed).
The diverter D can use a diverter line DL to communicate drilling fluid or mud from the riser R to a choke manifold CM, shale shaker SS or other drilling fluid receiving device. Above the diverter D can be the flowline RF which can be configured to communicate with a mud pit MP. A conventional flexible choke line CL can be configured to communicate with a choke manifold CM. The drilling fluid can flow from the choke manifold CM to a mud-gas buster or separator MB and a flare line (not shown). The drilling fluid can then be discharged to a shale shaker SS, and mud pits MP. In addition to a choke line CL and kill line KL, a booster line BL can be used.
After drilling operations, when preparing the wellbore and riser for production, it is desirable to remove the drilling fluid or mud. Removal of drilling fluid is typically done through displacement by a completion fluid. Because of its relatively high cost this drilling fluid is typically recovered for use in another drilling operation. Displacing the drilling fluid in multiple sections is desirable because the amount of drilling fluid to be removed during completion is typically greater than the storage space available at the drilling rig for either completion fluid and/or drilling fluid.
In deep water settings, after drilling is stopped the total volume of drilling fluid in the well bore and the riser can be in excess of 5,000 barrels. However, many rigs do not have the capacity for storing 5,000 plus barrels of completion fluid and/or drilling fluid when displacing in one step the total volume of drilling fluid in the well bore and riser. Accordingly, displacement is typically done in two or more stages.
Where the displacement process is performed in two or more stages, there is a risk that, during the time period between stages, the displacing fluid will intermix or interface with the drilling fluid thereby causing the drilling fluid to be unusable or require extensive and expensive reclamation efforts before being usable.
It is believed that rotating the drill string during the displacement process helps to better remove the drilling fluid along with down hole contaminants such as mud, debris, and/or other items.
It is believed that reciprocating the drill string during the displacement process also helps to loosen and/or remove unwanted downhole items by creating a plunging effect. Reciprocation can also allow scrapers and/or brushes to better clean desired portions of the walls of the well bore and casing, such as where perforations will be made for later production.
During displacement there is a need to allow the drilling fluid to be displaced in two or more sections.
During displacement there is a need to prevent intermixing of the drilling fluid with displacement fluid.
During displacement there is a need to allow the drill string to rotate.
During displacement there is a need to allow the drill string to reciprocate longitudinally.
While certain novel features of this invention shown and described below are pointed out in the annexed claims, the invention is not intended to be limited to the details specified, since a person of ordinary skill in the relevant art will understand that various omissions, modifications, substitutions and changes in the forms and details of the device illustrated and in its operation may be made without departing in anyway from the spirit of the present invention. No feature of the invention is critical or essential unless it is expressly stated as being “critical” or “essential.”